WHEN Dwayne and Mercedes Rivera got married October 2002, they, like most newlyweds, moved into a place of their own. the Riveras’ case, however, their love nest was a studio rental in Hartsdale.

But this isn’t a horror story.

“It was great – there was nowhere for her to run,” says Dwayne, 34.

Plus, “That’s how we ended up with him,” he jokes, pointing to their 1-year-old son, Noah.

Still, though they were comfortable in a studio, Dwayne had long harbored the dream of home ownership. And just as soon as they settled into their studio, the couple began looking for a house to buy.

“He was more into says Mercedes, 31, a credit executive. “But I cared, too.”

Nearly every weekend included an open house or . Over the course of 2 1/2years, the couple saw dozens and dozens of houses (“Like 100,” by Mercedes’ account, while Dwayne estimates closer to 60.)

“We were looking mostly (2) to find out about houses, but we were never convinced,” Mercedes says.

“There was always something wrong or it was too expensive.”

Way back at the very beginning of their search, the pair looked at a one-family house in Hartsdale, just down the street from their studio. It had an asking price of $429,000.

“We didn’t consider buying it,” says Dwayne. “We had just gotten married and just started looking.”

Ah, that laser-sharp vision called hindsight. Two years later, the Riveras saw the same house again -this time with a price tag of “$750-something,” says Dwayne.

It was the wake-up call that jolted the Riveras into action.

“We saw how much real estate had jumped, and we thought we have to make a move or else we won’t be able to afford anything,” Dwayne explains.

By this spring, the couple got serious about their search and determined some must-haves. First of all, since they owned three cars, a garage or ample room for parking was necessary. Second, the Riveras narrowed their search to two-family houses, figuring with the added rental income they could afford a bigger house in a better neighborhood.

Unfortunately, out in Westchester, “Finding a two-family house was like looking for a diamond in the rough,” says Dwayne, knowingly employing the real estate cliché. The handful of two-families they saw within their price range ($600,000 to $850,000) were generally on busy avenues and didn’t have any of the trappings of a suburban home, like a backyard or peace and quiet.

But one afternoon in early June, Dwayne was driving home through the Colonial Heights section of Yonkers. A “for sale” sign outside a corner house (read: expansive lawn) caught his eye -and the home, it turned out, was a two-family. It was love at first sight.

The Riveras offered $610,000, which was accepted. They closed July 20.

As first-time landlords, the couple got a pleasant surprise. The first-floor unit had a perfect tenant who was happy to stay put; and the house’s seller, who lives in Florida but travels to New York frequently, asked to rent the top floor. On the ground floor, in a one-bedroom, Dwayne, Mercedes and Noah live happily and cozily. Down the line, with plans to have more little ones, the Riveras envision renting the basement apartment to a relative and using their equity to buy a house of their very own.

“It’s a stepping stone for us,” says Dwayne.

Though it may merely be a stepping stone for the couple, for their young son, it’s quite literally a stepping ground. Out in the springy, lush lawn – freshly mowed by Dad – Noah’s been busy practicing his first steps.